Cisco IOS DHCP Relay Agent

DHCP is often used for hosts to automatically assign IP addresses and uses 4 different packets to do so. Since a host doesn’t have an IP address to start with, we use broadcast messages on the network that hopefully end up at a DHCP server.

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Cisco IOS SPAN and RSPAN

Cisco Catalyst Switches have a feature called SPAN (Switch Port Analyzer) that lets you copy all traffic from a source port or source VLAN to a destination interface. This is very useful for a number of reasons:

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Introduction to SNMP

Imagine you have a large network that has many switches and routers, a dozen servers and hundreds of workstations…wouldn’t it be great if you could monitor all those devices somehow? Using a NMS (Network Management System) it’s possible to monitor all devices in your network. Whenever something bad happens (like an interface that goes down) you will receive an e-mail or text message on your phone so you can respond to it immediately.

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How to configure SNMPv3 on Cisco IOS Router

SNMPv3 is similar to SNMPv1 or SNMPv2 but has a completely different security model. SNMPv1 and SNMPv2 use a community-string that is used as the password and there’s no authentication or encryption.

SNMPv3 is able to use both authentication and encryption and has a new security model that works with users, groups and 3 different security levels. Users will be applied to a group and access policies will be applied to a group so that you can determine what groups have read or read-write access and which MIBs (Management Information Bases) they should be able to access.

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Introduction to Cisco NetFlow

Network management protocols like SNMP allow us to monitor our network. We can check things like cpu load, memory usage, interface status and even the load of an interface. Other tools like NBAR allow us to see what kind of protocols are used.

One of the things we can’t do with those tools is tracking all flows in our network. A flow is a stream of packets that share the same characteristics like source/destination port, source/destination address, protocol, type, service marking, etc.

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Cisco Network Time Protocol (NTP)

TP (Network Time Protocol) is used to allow network devices to synchronize their clocks with a central source clock. For network devices like routers, switches or firewalls this is very important because we want to make sure that logging information and timestamps have the accurate time and date. If you ever have network issues or get hacked, you want to make sure you know exactly what and when it happened.

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Bidirectional Forwarding Detection (BFD)

BFD (Bidirectional Forwarding Detection) is a super fast protocol that is able to detect link failures within milliseconds or even microseconds.. All (routing) protocols have some sort of mechanism to detect link failures. OSPF uses hello packets and a dead interval, EIGRP uses hello packets and a holddown timer etc.

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